Conventionally, electroconductive compositions that can be dried and cured at 200° C. or less are often obtained, for example, as a result of mixing an electroconductive powder with thermoplastic resins such as polyester resins and acrylic resins, or with thermosetting resins such as epoxy resins and urethane resins, and then mixing the product with a suitable solvent.
However, with paste compositions obtained as a result of mixing an electroconductive powder with the usual thermoplastic resins or thermosetting resins, the resistivity of a film obtained by means of drying and curing the compositions is not sufficiently low, and is usually 10−5 Ω·cm or greater. The increase in film resistivity poses a problem, particularly during the formation of thin electroconductive wirings from those paste compositions. Further, films obtained by means of drying and curing such pastes are known to have poor solderability. In order to improve solderability, use of specific electroconductive powders, such as silver coated powders, silver-copper alloy powders, and graded material powders has been suggested (see Patent Documents 1 to 3)
To obtain a film of lower resistivity, baking-type electroconductive paste compositions are commonly used. Baking-type electroconductive paste compositions are compositions commonly containing electroconductive powders, glass frit, and dispersants. The baking-type electroconductive paste compositions yield films having a resistivity of about 10−6 Ω·cm, but they require that baking be conducted at temperatures of at least 500° C. or greater to achieve this level of resistivity.
In recent years, the use of finer electroconductive powders (all the way to the nanosize) made it possible to perform baking at a temperature of about 200° C., and baking-type electro-conductive paste compositions capable of forming coating films with a resistivity of about 10−6 Ωcm have been proposed (see Patent Document 4). It has also been proposed to use electroconductive paste compositions that are obtained as a result of mixing finer silver oxide powders (all the way to the nanosize) and tertiary fatty acid silver salts, and that are capable of forming low-resistance films at low temperatures (see Patent Document 5).
Document 1JP (Kokai) 07-014429Document 2JP (Kokai) 06-215617Document 3JP (Kokai) 06-052721Document 4JP (Kokai) 2002-299833Document 5JP (Kokai) 2003-203622